Hello,

My simple code is here:

Public Class MyDictionary
Inherits System.Collections.DictionaryBase

Private Class MyElement
Public Overloads Overrides Function Equals(ByVal obj As Object) As Boolean
End Function
End Class

Public Sub Add(<params>)
If Not dictionary.Contains(MyElementObject) Then
End If
End Sub
End Class


Do you know why the Equals method never gets called please?

Thank you, regards, dnw.

Dnw,
Does MyElementObject represent a Value or a Key in the Dictionary?

Within DictionaryBase 'dictionary.Contains' "determines whether the
IDictionary contains an element with the specified key", hence if
MyElementObject represents a Value, Contains is always going to return
false...

If MyElementObject represents a Key, then it needs to override both
Object.Equals & Object.GetHashCode, as a Dictionary requires both to be
implemented.

For example:

Dim dictionary As New Hashtable
dictionary.Add(New KeyPair("A", "B"), "A value")
Debug.WriteLine(dictionary.Contains(New KeyPair("A", "B")),
"contains key pair")
Debug.WriteLine(dictionary.Contains("A value"), "contains a value")


Public Class KeyPair

Private ReadOnly m_value1 As String
Private ReadOnly m_value2 As String

Public Sub New(ByVal value1 As String, ByVal value2 As String)
m_value1 = value1
m_value2 = value2
End Sub

Public Overrides Function GetHashCode() As Integer
Return m_value1.GetHashCode() Xor m_value2.GetHashCode()
End Function

Public Overloads Overrides Function Equals(ByVal obj As Object) As
Boolean
If Not TypeOf obj Is KeyPair Then Return False
Dim other As KeyPair = DirectCast(obj, KeyPair)
Return m_value1 = other.m_value1 AndAlso m_value2 =
other.m_value2
End Function

End Class

Also its better that Equals & GetHashCode are based on readonly fields as I
have done above, otherwise you run the risk of returning inconsistent values
for Equals & GetHashCode which will cause even more confusion (for the
dictionary & you).

Hope this helps
Jay

"Dot net work" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Hello,
>
> My simple code is here:
>
> Public Class MyDictionary
> Inherits System.Collections.DictionaryBase
>
> Private Class MyElement
> Public Overloads Overrides Function Equals(ByVal obj As Object) As
> Boolean
> End Function
> End Class
>
> Public Sub Add(<params>)
> If Not dictionary.Contains(MyElementObject) Then
> End If
> End Sub
> End Class
>
>
> Do you know why the Equals method never gets called please?
>
> Thank you, regards, dnw.

Awesome! You are a ninja programmer!

"Jay B. Harlow [MVP - Outlook]" <(E-Mail Removed)> wrote in message news:<e9H#(E-Mail Removed)>...
> Dnw,
> Does MyElementObject represent a Value or a Key in the Dictionary?
>
> Within DictionaryBase 'dictionary.Contains' "determines whether the
> IDictionary contains an element with the specified key", hence if
> MyElementObject represents a Value, Contains is always going to return
> false...
>
> If MyElementObject represents a Key, then it needs to override both
> Object.Equals & Object.GetHashCode, as a Dictionary requires both to be
> implemented.
>
> For example:
>
> Dim dictionary As New Hashtable
> dictionary.Add(New KeyPair("A", "B"), "A value")
> Debug.WriteLine(dictionary.Contains(New KeyPair("A", "B")),
> "contains key pair")
> Debug.WriteLine(dictionary.Contains("A value"), "contains a value")
>
>
> Public Class KeyPair
>
> Private ReadOnly m_value1 As String
> Private ReadOnly m_value2 As String
>
> Public Sub New(ByVal value1 As String, ByVal value2 As String)
> m_value1 = value1
> m_value2 = value2
> End Sub
>
> Public Overrides Function GetHashCode() As Integer
> Return m_value1.GetHashCode() Xor m_value2.GetHashCode()
> End Function
>
> Public Overloads Overrides Function Equals(ByVal obj As Object) As
> Boolean
> If Not TypeOf obj Is KeyPair Then Return False
> Dim other As KeyPair = DirectCast(obj, KeyPair)
> Return m_value1 = other.m_value1 AndAlso m_value2 =
> other.m_value2
> End Function
>
> End Class
>
> Also its better that Equals & GetHashCode are based on readonly fields as I
> have done above, otherwise you run the risk of returning inconsistent values
> for Equals & GetHashCode which will cause even more confusion (for the
> dictionary & you).
>
> Hope this helps
> Jay
>
> "Dot net work" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> > Hello,
> >
> > My simple code is here:
> >
> > Public Class MyDictionary
> > Inherits System.Collections.DictionaryBase
> >
> > Private Class MyElement
> > Public Overloads Overrides Function Equals(ByVal obj As Object) As
> > Boolean
> > End Function
> > End Class
> >
> > Public Sub Add(<params>)
> > If Not dictionary.Contains(MyElementObject) Then
> > End If
> > End Sub
> > End Class
> >
> >
> > Do you know why the Equals method never gets called please?
> >
> > Thank you, regards, dnw.